Multi-fuel, combined cycle power plant

ABSTRACT

A power plant includes a gas turbine unit having a compressor for compressing ambient air, a burner for burning fuel and heating air compressed by said compressor, and a turbine for expanding air heated by said burner to drive said compressor and produce hot exhaust gases. The plant further includes a combustor for containing particles of solid fuel which are fluidized by the exhaust gases from the turbine to produce hot products of combustion that include coarse ash particulate. Apparatus is provided for generating power from the hot products of combustion.

This is a divisional of Ser. No. 08/834,125 filed Apr. 14, 1997, nowabandoned, which is a continuation of Ser. No. 08/329,060 filed Oct. 11,1994, now abandoned.

TECHNICAL FIELD

This invention relates to a multi-fuel, combined cycle power plant.

BACKGROUND

For many years, large scale gas turbine based stationary power plantsfueled by conventional gas or liquid fuels, such as natural gas,liquefied petroleum gas (LPG), etc., have been used by utilities forpeaking purposes because of the fast, on-line response of a gas turbine.

More recently, combined cycle power plants have been constructed toincrease the efficiency of the system thus enabling the gas turbine tobe incorporated into power plants that provide base load electric power.Such power plants include a waste heat boiler that extracts heat fromthe exhaust gases of the gas turbine for generating steam that drives asteam turbine and produces additional power. Furthermore, sometimessupplementary duct firing has been used as an addition to the waste heatboiler.

At the same time, efforts have been made to utilize less expensive, andmore abundant low heat content solid fuels, such as low quality coal,oil shale, bituminous phosphates, biomass, etc., in base-line powerplants. Conventionally, power plants using such low heat content fuelshave employed fluidized bed combustors that include integral heattransfer elements. Such elements are usually rapidly fouled byagglomeration of ash because the solid fuels used contain relativelylarge amounts of ash, and this complicates heat transfer to the workingfluid of the power plant.

It is an object of the present invention to provide a combined cyclepower plant operating on low quality solid fuel in which several of thedisadvantages outlined are reduced or substantially overcome.

DISCLOSURE OF INVENTION

A power plant according to the present invention includes a gas turbineunit having a compressor for compressing ambient air, a burner forburning fuel under excess air conditions and heating air compressed bythe compressor, a generator, and a turbine coupled to a generator forexpanding air heated by the burner to drive the compressor and thegenerator for producing hot exhaust gases and electrical power. Theplant further includes a combustor, for supplementary firing of theexhaust gases burning particles of solid fuel which are fluidized by theexhaust gases from the turbine and which produce hot products ofcombustion that include coarse ash particulate. Apparatus is providedfor generating power from the hot products of combustion.

Preferably, the fluidization of the particles in the combustor isachieved in a spouted bed combustor that includes a separator forextracting coarse ash particulate from the hot products of combustion.In such case, the apparatus for generating power from the hot productsof combustion includes a waste heat boiler responsive to the hotproducts of combustion after the separator extracts coarse ashparticulate for producing steam, a steam turbine coupled to a generatorfor expanding the steam and producing power, and a condenser unit forcondensing steam expanded in the steam turbine. A pump may be providedfor returning the condensate produced by the condenser to the waste heatboiler.

Separation, and/or precipitation filtering, of much of the ashparticulate from the products of combustion before these products areapplied to the waste heat boiler significantly reduces fouling of theheat transfer elements in the boiler. Moreover, under these conditions,a spouted bed combustor is advantageous over a fluidized bed combustorin that a spouted bed combustor is less sensitive to variations in flowrate through the gas turbine unit which occur under certain conditionsof use.

If little or no water is available, an air-cooled condenser can be used.In such case, the condenser unit of the waste heat boiler preferablycontains an organic fluid that is vaporized by the condensing steam forproducing vaporized organic fluid, and an organic vapor turbine coupledto a generator is provided to produce power by expanding the vaporizedorganic fluid. The expanded vaporized organic fluid is condensed to aliquid in the air-cooled condenser; and a pump or gravitationalassistance may be provided for returning the condensed liquid to theorganic condenser.

When a spouted bed combustor is utilized, the power plant according tothe invention preferably includes a pyrolyzer adapted to contain crushedoil shale, or other solid fuel, or mixture of fuels, and to receive ashextracted by the separator for producing a carbonaceous residue that issupplied to the spouted bed combustor, and combustible products. Thecombustible products in the form of combustible gases may bemechanically filtered and then pressurized before being applied to theburner of the gas turbine unit. Alternatively, the combustible productsmay be treated to produce clean, treated combustibles gases that areapplied to the burner, and liquid fuel that may be added to a combustorlike a spouted bed combustor. Finally, when a fluidized bed combustor isemployed, an auxiliary heat exchanger associated with the combustor maybe utilized for exchanging heat between combustor and air compressed bythe compressor upstream of said burner.

If an appropriate fluidized bed combustor is used instead of a spoutedbed combustor, the heat exchanger would be mounted within the combustionsection. When a spouted bed combustor is used, the heat exchanger is aunit separate from the combustor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are shown by way of examples in theaccompanying drawings wherein:

FIG. 1 is a block diagram of a power plant according to the presentinvention showing a gas or liquid fueled gas turbine unit that fluidizesa spouted bed combustor supplying products of combustion to a waste heatboiler;

FIG. 2 is a block diagram of a power plant like that shown in FIG. 1 butincorporating a pyrolyzer for supplying combustible gas to the gasturbine unit;

FIG. 3 is a block diagram of a power plant like that shown in FIG. 1 inwhich the air compressed by the compressor of the gas turbine unit isheated in a waste heat boiler, and then topped by using gaseous orliquid fuel in a separate burner;

FIG. 4 is is a block diagram of a power plant like that shown in FIG. 3but incorporating a pyrolyzer for supplying combustible gas to the gasturbine unit;

FIG. 5 is a schematic showing of a fluidized bed suitable for use in thepresent invention;

FIG. 6 is a block diagram of a power plant according to the presentinvention showing a conventional fluidized bed supplied with fuel from apyrolyzer, and showing topping off of the air compressed by thecompressor of the gas turbine unit using heat in the fluidized bed; and

FIG. 7 is a modification of the power plant shown in FIG. 6.

DETAILED DESCRIPTION

Referring now to the drawings, reference numeral 10 designates oneembodiment of a power plant according to the present invention andspecifically, a multi-fuel combined cycle power plant. Plant 10comprises gas turbine unit 12 having compressor 14 for compressingambient air entering the compressor at 15, burner 16 for heating aircompressed by the compressor, generator 36, and turbine 18 for expandingair heated by the burner to drive the compressor and generator,producing electric power and hot exhaust gases that exit the turbine at19. Usually, external source of fuel 20 (preferably, natural gas,liquefied petroleum gas (LPG), or kerosene) is provided for supplyingfuel to burner 16 of unit 12 where the fuel burns in excess air.

Plant 10 also includes a combustor, which may be a fluidized bedcombustor, but preferably is a spouted bed combustor indicated byreference numeral 22, for containing particles 23 of solid fuel. Aspouted bed combustor is described in Spouted Beds by K. B. Mathur andN. Epstein, Academic Press, 1974, which is hereby incorporated byreference. Alternatively, combustor 22 may be another type of suitablecombustor.

Spouted bed combustors are presently considered advantageous for thecombustion of oil shale because of the recirculation of ash andcarbonaceous material which occurs in the combustor. Such recirculationensures adequate heating of fresh oil shale supplied to the combustor sothat substantially all of the organic material present in the oil shaleis converted into vapor for combustion. A further advantage of a spoutedbed combustor is the placement of a heat exchanger for producing, forexample, steam, outside of the combustion chamber. This allows ash inthe products of combustion produced by the spouted bed combustor to beremoved before such products are applied to a heat exchanger thusinhibiting its fouling.

Particles 23 in combustor 22 are fluidized with the exhaust gases inline 19 connected to the exhaust of turbine 18. The particles burn inthe combustor producing in outlet 24, hot products of combustion thatinclude coarse ash particulate, fine ash, and hot flue gases. While thedrawing shows the turbine exhaust gases being used to fluidize particles23 in the spouted bed combustor, a portion of these gases also can beinput to other portions of combustor 22 for improving the combustionconditions, or to waste boiler 26 for improving its performance.Alternatively, in this embodiment, and in the other embodiments of thepresent invention as well, a portion of the turbine exhaust gases can beused for heating an organic fluid which can be used for producing power.

Combustor 22 also includes separator 25 for extracting ash particulatefrom the hot products of combustion produced by the combustor; and means26 are provided for generating power in response to the hot products ofcombustion. In plant 10, means 26 are in the form of waste heat boiler26, steam turbine 27, and steam condenser unit 28. Boiler 26 isphysically separate from spouted bed combustor 22 and responsive to thehot products of combustion after separator 25 extracts coarse ashparticulate for producing steam that is applied via line 29 to steamturbine 27. Expansion of the steam in turbine 27 drives generator 30 andproduces power. Finally, condenser unit 28 serves to condense steamexpanded in the steam turbine producing steam condensate that isreturned by pump 31 to the waste heat boiler. As indicated, fan 32associated with the waste heat boiler is provided between the outlet ofthe waste heat boiler and the stack (not shown) for enhancing the flowof the products of combustion through heating coils 37 carrying water,and also for reducing the back pressure on the exit of the gas turbine.

Preferably, condenser unit 28 includes condenser 34 that is a part oforganic Rankine cycle power module 38. Condenser 34 contains an organicfluid, preferably pentane, that is vaporized by the condensing steam forproducing vaporized organic fluid, and organic vapor turdine 38 forexpanding the vaporized organic fluid and producing power and expandedorganic vapor. Module 38 of unit 28 includes organic vapor condenser 39,which preferably, is air cooled for condensing the expanded organicfluid to a liquid. The organic liquid condensate may be returned tocondenser 34 by pump 35, or by gravity utilizing the hydraulic head ofthe liquid if the elevation of condenser 39 is sufficiently abovecondenser 34.

Hot ash separated by separator 25 from the products of combustionproduced by the spouted bed combustor may be used to heat the pulverizedsolid fuel before it is fed to the spouted bed combustor. This optionalarrangement is indicated by the block marked “drier”.

When a spouted bed combustor is used in accordance with the presentinvention, additional air, if needed, may be supplied to the combustionchamber to increase the volumetric flow of heated air. Such heated aircan be used for heating purposes such as heating compressed air using anindirect heat exchanger. Alternatively, the air can be supplied directlyto the turbine of a gas turbine. Also here, when an indirect heatexchanger is used, a ceramic heat exchanger advantageously can be used.In addition, when the hot air exiting combustion chamber is useddirectly (i.e., without heat exchanger surfaces being utilized), ceramicfilters can be employed.

While a spouted bed combustor is shown schematically in FIG. 1, aconventional fluidized bed combustor can also be used. However, therange of air flow over which a spouted bed combustor will worksuccessfully is greater than the range of flow for a conventionalfluidized bed combustor. Thus, a spouted bed combustor is more suitablewhen there is a wide variation in flow rates and in types of solid fuelthat is utilized due, for example, to daily and/or seasonal changes. Aspouted bed combustor has other advantages as described below whentopping of the compressed air is employed.

In operation, ambient air is compressed in compressor 14 producingcompressed air that is heated by the burning of liquid or gaseous fuelin burner 16, combustion taking place under conditions of excess airproducing hot gases that expand in turbine 18 driving generator 36. Theexhaust gases fluidize solid fuel particles 23 which are fed to thecombustion chamber of spouted bed combustor 22 from source 37A ofpulverized fuel (e.g., crushed oil shale) where the fuel burns producinghot products of combustion that include coarse particulate, fine ash,and hot gases. After the coarse particulate are separated from theproducts of combustion by cyclone separator 25, the remaining hotproducts of combustion are applied to waste heat boiler 26 containingheat transfer coils 37. Water in these coils is heated, vaporized, andsuperheated before being applied to steam turbine 27 wherein expansiontakes place driving generator 30. Condensation takes place in condenserunit 34, and pump 31 returns the condensate to waste heat boiler 26.Finally, additional power is generated by condensing the steam incondenser unit 28 using an organic Rankine cycle power plant asdescribed above.

In plant 10 described above, crushed solid fuel is fed directly tospouted bed combustor 22. However, the present 15 invention alsocontemplates treating crushed solid fuel in a pyrolyzer before the fuelis fed to the spouted bed combustor as shown in plant 40 of FIG. 2. InFIGS. 1 and 2, like reference numerals are applied to like components.In plant 40 of FIG. 2, crushed oil shale from source 42 is applied topyrolyzer 43 which also receives hot, coarse particulate from cycloneseparator 25. In the oxygen free atmosphere contained within thepyrolyzer, organic material in the crushed oil shale producescombustible products that are drawn from the pyrolyzer via line 44.Carbonaceous residue 45 from the pyrolyzer is fed to spouted bedcombustor 22. Ash produced by the combustion process in the spouted bedcombustor is continuously removed from the combustor.

Preferably, heat contained in the combustible products produced bypyrolyzer 43 may be used to supplement the heating of the compressed airproduced by compressor 14. Thus, the combustible products may be applieddirectly to burner 16, wherein they are burned together with preferablynatural gas, or LPG, or liquid fuels, or, the combustible products firstcan be applied to gas treatment system 46 for the purpose of filteringor further treating the combustible products.

Gas treatment system 46 is a schematic representation of apparatus forpre-treating the combustible products of the pyrolyzer for producinguseful fuel. System 46 may comprise a ceramic filter which serves toextract fine particulate from the combustible products and produce fuelin the form of clean combustible gas at high temperature. Alternatively,the combustion products of the pyrolyzer can be filtered by passing theproduct through liquid bath, such as water. The combustible products maycondense in the liquid, allowing filtration to take place beforecombustion occurs. Alternatively, the combustion products can befiltered in hydrocarbon liquid which cools the products to between200°-300° C. before the filtered products are combusted.

The fuel produced by system 46 can be used in the power plant for anumber of purposes. Preferably, clean combustible gas produced by system46 is fed to burner 16; and in such case, element 47 associated withsystem 46, represents a compressor which pressurizes the cleancombustible gas to effect its entry into burner 16. Also, combustibleliquid fuel produced by system 46 can be fed to burner 16 afterfiltering; and in this case, a pump can be used for supplying the cleanliquid to burner 16. Alternatively, this combustible liquid can besupplied, unfiltered, to spouted bed combustor 22, or a fluidized bedcombustor if used. Optionally, some of the combustible products producedby the pyrolyzer can be fed, unfiltered, directly to spouted bedcombustor 22, or fluidized bed if used.

The operation of plant 40 so far as gas turbine unit 12 and waste heatboiler 26 are concerned is substantially the same as previouslydescribed in connection with plant 10. The significant difference inplant 40 over plant 10 is the provision of pyrolyzer 43, and optionalgas treatment system 46 for the purpose of supplementing heat added byburner 16 to air compressed by compressor 14.

Topping of the heat added to the compressed air in gas turbine unit 12,which is achieved in plant 40 by the combustion of the combustibleproducts produced by the pyrolyzer, can be achieved in a plant likeplant 10 in the manner shown in FIG. 3 to which reference is now made.Plant 50 shown in FIG. 3 is similar to plant 10 shown in FIG. 1 exceptfor the topping feature to be described. Like reference numerals in FIG.3 are applied to like components shown in FIG. 1. In FIG. 3, heating ofthe air compressed in compressor 14 is achieved by the provision ofmeans for exchanging heat upstream of the burner between waste heatboiler 26A and air compressed by the compressor. Specifically, as shownin FIG. 3, waste heat boiler 26A is provided with heat exchange coils 52through which air compressed by compressor 14 passes thereby heating thecompressed air before it is applied to burner 16A. If the heat suppliedto the air compressed by compressor 14 by coils 52 is not adequate,preferably natural gas, or LPG, or liquid fuels such as kerosene, etc.also may be burned in burner 16A to top the heat supplied by coils 52.

The use of gaseous or liquid fuels for heating the air compressed by thecompressor of the gas turbine unit can be dispensed with in thearrangement shown in plant 60 of FIG. 4 to which reference is now made.Plant 60 is similar to plant 40 and like reference numerals in FIGS. 2and 4 are applied to like components. In plant 60, waste heat boiler 26Ais provided with heat exchange coils 62 through which air compressed bycompressor 14 passes before being applied to burner 16A. Gas treatmentsystem 46 receives the combustible products produced by pyrolyzer 43 andproduces clean gaseous fuel, or a combination of clean gaseous fuel andliquid fuel as described above; and such fuel may be fed to burner 16Ain the manner described above. Thus, the compressed air produced bycompressor 14 is heated by both heat extracted from waste heat boiler26A and by the heat produced by the combustible products produced by thepyrolyzer. In this embodiment, no conventional gaseous or liquid fuel isnecessary for the operation of the plant.

The above-described embodiments of the present utilize a spouted bedcombustor, but a conventional fluidized bed combustor could also be usedunder some circumstances. This arrangement is illustrated in FIG. 5where fluidized bed combustor 70 is illustrated having the coils 72 inthe combustion chamber. These coils contain water that is converted tosteam which is supplied to a steam turbine. Coils 72 are shownschematically and represent the preheating, vaporization, and superheating coils that would be associated with a fluidized bed combustor.

When a fluidized bed is used, the hot exhaust gases from the gas turbineunit are applied as indicated at 74 a purpose of fluidizing the contentsof the combustion chamber. Crushed solid fuel, such as crushed oilshale, for example, is applied to the fluidized bed from source 76, andthe fluidizing operation is achieved by reason of the fluidizing air/gasmixture supplied by the exhaust of the gas turbine unit and by auxiliaryfan 78 which supplies supplementary fluidizing air to the combustionchamber.

Instead of directly supplying crushed solid fuel to the fluidized bedcombustor shown in FIG. 5, a pyrolyzer may be utilized as illustrated byplant 80 in FIG. 6 to which reference is now made. As shown in FIG. 6,pyrolyzer 82 receives crushed oil shale from source 81 thereof andreceives hot coarse ash particulate from fluidized bed combustor 84. Thepyrolyzer produces a carbonaceous residue which is applied to thefluidized bed and also produces combustible products which may beapplied directly to burner 16B associated with gas turbine units 12.Optionally, the combustible products may be treated as described abovebefore combustion takes place in burner 16B.

Burner 16B receives air compressed by compressor 14 of gas turbine unit12 after the air passes through heat transfer coils 86 contained withinthe combustion chamber of the fluidized bed. The heated air is nowapplied to the burner where the combustible products from pyrolyzer 82are burned thereby heating the air applied to turbine 18. The exhaustfrom this turbine is applied as a fluidizing air/gas mixture tofluidized bed 84 as indicated in the solid lines in the drawing.

Optionally, as shown by the broken lines in FIG. 6 some of the exhaustgases from turbine 18 may be applied to indirect heat exchanger 87before being exhausted to a suitable stack. Heat exchanger 87 includesheat exchange coils 88 containing an organic fluid which is vaporized bythe exhaust gases from the turbine producing vaporized organic fluidwhich is applied to organic turbine 89 wherein expansion takes drivinggenerator 90 and producing expanded organic vapor in line 91. Theexpanded organic vapor is condensed in air condenser 92 and thecondensate is returned by pump 93 to coils 88 completing the organicfluid cycle.

Instead of generating power using an organic fluid as shown in FIG. 6,steam can be used for generating the power as illustrated in FIG. 7 towhich reference is now made. Plant 100 shown in FIG. 7 is similar to theplant 80 shown in FIG. 6 and like reference numerals in each of thesefigures denote like components. In FIG. 7, coils 86 in the combustionchamber of fluidized bed 84 provide heat for heating the compressed airproduced by compressor 14. Topping of this air may be achieved by beatproduced by the combustion of combustible products produced by pyrolyzer82 in burner 16B.

Fluidized bed 84 also includes preheater coils 102, vaporizer coils 104,and super heater coils 106 by which water is sequentially preheated,vaporized and then super heated by reason of the combustion processeffected in fluidized bed 84. Super heated steam produced by superheater coils 106 is applied to steam turbine 108 where expansion takesplace driving generator 110 and producing expanded steam in line 112.Air cooled condenser 114 is provided for condensing the expanded steamproduced by the steam turbine and producing a condensate which isreturned by pump 116 to preheater coils 112 completing the water cycleof the power plant.

In the embodiments of the invention utilizing a pyrolyzer, crushed oilshale is shown as being added to the pyrolyzer, and the carbonaceousresidue from the pyrolyzer is shown as being fed to a spouted bedcombustor. In a modification, crushed oil shale as well as thecarbonaceous residue from the pyrolyzer can be added directly to thespouted bed combustor. Moreover, other low heat content fuels, such aspeat, can be used in place of, or combined with oil shale in the variousembodiments of the invention described above. In addition, such low heatcontent fuels can be combined with sulfur rich materials like sulfurrich fuel, e.g., high sulfur fuel oil and used together in the presentinvention by mixing or separately adding the fuels to the pyrolyzer, tothe spouted bed combustor, or to the fluidized bed in the variousembodiments.

Furthermore, the operation of a pyrolyzer and combustor disclosed in thevarious embodiments disclosed above produces less NOx gases because sucha system is staged. In addition, the operating temperatures in thepyrolyzer and in the combustor are preferably less than 1000° C. whichalso reduces the production of NO_(x) gases.

Finally, the present invention is particularly well adapted torelatively small power plants, i.e., plants up to about 30 MW. Thus, theinvention provides an efficient, cost effective, and non-polluting wayto produce electricity at many location throughout the world.

The advantages and improved results furnished by the method andapparatus of the present invention are apparent from the foregoingdescription of the preferred embodiment of the invention. Variouschanges and modifications may be made without departing from the spiritand scope of the invention as described in the appended claims.

What is claimed:
 1. A power plant comprising: a) a gas turbine unithaving a compressor for compressing ambient air, a burner for heatingair compressed by said compressor, a generator, and a turbine coupled tothe compressor and to said generator for expanding air heated by saidburner to drive said compressor and generator such that the turbineproduces hot exhaust gases and the generator produces electricity; b)means for supplying fuel to said burner; c) a combustor for containingparticles of solid fuel; d) means applying said exhaust gases to saidcombustor for fluidizing and combusting said particles in said combustorto produce hot products of combustion that include coarse ashparticulate; e) a separator for separating ash particulate from saidproducts of combustion and producing separated products of combustion;f) a waste heat boiler, separate from said combustor, responsive to saidseparated products of combustion for producing steam; g) means forsupplying solid fuel to said combustor; h) a steam turbine for expandingsaid steam and producing power; i) a steam condenser unit for condensingsteam expanded in said steam turbine; j) means for returning thecondensate produced by said condenser unit to said waste heat boiler;and k) a pyrolyzer adapted to contain crushed oil shale for receivingash extracted by said separator and producing a carbonaceous residuethat is supplied to said combustor.
 2. The power plant according toclaim 1 wherein said combustor is a spouted bed combustor.
 3. The powerplant according to claim 1 wherein said combustor is a fluidized bedcombustor.
 4. The power plant according to claim 1 wherein said meansfor supplying fuel to said burner supplies natural gas.
 5. The powerplant according to claim 1 including a heat exchanger responsive to saidhot products of combustion for heating the compressed air before saidcompressed air is supplied to said burner.
 6. A power plant according toclaim 5 including a separator for separating ash particulate from saidproducts of combustion before they are supplied to said heat exchanger.7. A power plant according to claim 1 wherein said pyrolyzer producescombustible products that are supplied to said burner.
 8. The powerplant according to claim 1, wherein the waste heat boiler is part of athermal water fluid cycle containing water fluid which produces heatedwater fluid, the heat contained in the heated water fluid beingtransferred to an organic working fluid condensate via a heat exchangesystem.
 9. The power plant according to claim 8, further comprising aclosed Rankine cycle power plant having said heat exchange systemincluding a vaporizer which vaporizes an organic working fluid andproduces an organic working fluid vapor using heat contained in said hotexhaust gases, an organic vapor turbine which expands the organicworking fluid vapor and produces power and expanded organic workingfluid vapor, an organic fluid condenser which condenses the expandedorganic working fluid vapor and produces said organic working fluidcondensate whereby said organic working fluid condensate is returned tothe vaporizer.
 10. The power plant according to 8 where the organicworking fluid is pentane.